Method of insulating conductors



De-c.'28, 1937. J. F. CALVERT 2,103,841

METHOD OF INSULATING CONDUCTORS Filed Jan. 50, 1957 WlTNESSES: INVENTORJob/7 Ca/l/erz Patented Dec. 28, .1937

UNITED STATES PATENT OFFICE John F. Calvert, Ames, Iowa, assignor toWestinghouse Electric 8: Manufacturing Company,

syl

East Pittsburgh, Pa., a corporation of Pennvania Application January 30,1937, Serial No. 123,243

' 8 Claims.

o the insulating material, a part of the bonding material is lost in theform of a vapor before the material is suiiiciently polymerized to thenonvolatile state. The escaping vapor tends to leave voids in theinsulation. Such non-uniformly in-' sulated conductors .are dangerous.

An object of. this invention is to provide a method of insulatingelectric conductors whereby the conductors will have a uniforminsulating coating.

A further object of this invention is to provide a method for preventingloss of insulating material by vaporization while insulating anelectrical conductor.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with the accompanying drawing, inwhich the single figure, partly in section and partly in side elevation,illustrates a conductor which is insulated in accordance with theteachings of this invention.

According to this invention, tape coverings or wrappings for electricalconductors are impregmated with self-polymerizing material and thecovered conductors are subjected to a treatment for polymerizing thematerial in the tape whereby a uniform insulating coating is providedfor the conductor.

In order to secure a satisfactory impregnation of the tape usuallyemployed in the insulating conductors, it has been found to be desirableto thoroughly cleanse the tape of resin and deleterious material beforethe self-polymerizing material is applied. In practice, tape comprisingpapenmica flakes and asphaltic sticking varnish may be cleansed bytreating the tape with benzol to extract the asphaltic varnish. Sincebenzol is quite volatile, it is easily removed by drying the tape.

The cleansed mica tape is impregnated with an insulating medium of theself-polymerizing tape which may be satisfactorily hardened.Selfpolymerizing materials which may be satisfactorily employed as theinsulating medium comprise styrol, such as monostyrene or a lowviscosity or fluid product of styrol such as a mixture of polymerizedproducts of styrene in liquid styrene. Other self-polymerizing materialswhich may also be employed are derivatives of acrylic acid or alphamethyl acrylic acid or derivatives of acrylic acid or alpha methylacrylic acid which are only slightly polymerized and fluid or have a lowviscosity.

In preparing the conductor to be insulated, the tape is impregnated inany suitable manner such as dipping or brushing with one of theselfpolymerizing materials hereinbefore mentioned. In order to stabilizethe impregnant and to prevent the polymerization of the material untildesired, an inhibitor such as hydroquinone is mixed in theself-polymerizing material. As illustrated in the drawing, tapeimpregnated with the selfpolymerizing material containing the inhibitoris wrapped around the conductor 10 constituting an inner layenorcovering l2, the reason of which will be explained more fullyhereinafter.

Since the impregnant is volatile and it is desired to prevent loss ofthe insulating materialby vaporization, additional tape is impregnatedwith the self-polymerizing material to form an outer layer or covering14 when wrapped on the conductor ID, as illustrated in the drawing. Inorder to accelerate the polymerization of the insulating material in theouter layer H to obtain the polymerization thereof without excessivelosses by. volatilization of the material, a catalyst such as benzoylperoxide is added to the self-polymerizing material before the tape isimpregnated.

In order to harden the outer layer [4, to prevent losses of theimpregnant of the layer I2 when heat treated, as described hereinafter,the tape wrapped conductor is heated to a sufficient temperature tocause the polymerization of the impregnant containing the catalyst inthe outer layer It. Through experience, it is found that Where the tapewrapped conductor is exposed to room temperature for a period of time ofa few hours, the self-polymerizing material in the outer layer Itbecomes hardened. The polymerization of the insulating material in theouter layer l4 may be further accelerated by heating briefly at slightlyhigher temperatures than room temperature.

In order to protect the wrappings of tape around the conductor II) whensubjected to heat and pressure to cause the polymerization of theinsulating material of the inner layer of tape, a protective covering [8of some suitable material such as cotton tape or cotton tape with a clayor powder on the surface adjacent the outer layer ll of tape iswrappedaround the exposed surface Gil or the hardened outer layer 14. Othersoft and pliable sheet material which may be easily wrapped around theconductor or applied to the conductor surface and held in place may beemployed as the protective covering.

In order to polymerize and harden the insulating material containing theinhibitor in the inner layer of tape, the wrapped conductor in itsprotective covering is immersed in hot asphalt orvother hot fluid in anautoclave and then sub- 'jected to heat and pressure for a predeterminedperiod of time sumcient to polymerize the impregnant. As a result ofhardening the outer layer of the tape around the conductor beforeimmersing the conductor in the hot asphalt and subjecting it to heat andpressure, the full hydrostatic pressure developed in the autoclave isexerted with equal force throughout the entire outer surface of thewindings of the conductor, producing a dense and uniform insulatingstruc-. ture around the conductor, When removed from the autoclave, theprotective covering may be removed from the insulated conductor wheredesired.

In practicing this invention, the tape comprising the different layersaround the conductor may be thoroughly impregnated with thesellpolymerizing materials containing the inhibitor or catalyst ashereinbeiore described and then wound around the conductor. Instead.- ofimpregnating the tape prior to winding the conductor, the conductor maybe wound with an unimpregnated layer oi tape and then the tapedconductor may be brushed with or dipped into the sell-polymerizingmaterial containing the in hibitor to thoroughly-impregnate it. An outerlayer of unimpregnated tape ,may then be wrapped around the impregnatedlayer, after which the wrapped conductor maybe brushed with or dippedinto the self-polymerizing mate rial containing the catalyst impregnatethe outer layer of tape.

m practicing this method, it is iound that there is very little loss oithe volatile seli-poly=' merining material by vaporization during thepolymerization process. This is because the hardened outer layer oi thetape prevents the escape of the impregnating material in the inner layeroi the tape when heat and pressure are applied thereto. Conductors whichhave been wrapped with tape impregnated with self-polymerizlng materialscontaining inhibitors and catalysts and polymerized, as hereinbeioredescribed, have been found to be uniformly insu= lated. h'nrther, thistype of insulation has been found to have a very low power factor and tobe quite hard at temperatures ranging between 90 C. and 12d (G.

While a specific method has been described embodying this invention, itis to be understood that this invention is not to be limited theretoexcept as is necessitated by the prior art and the scope oi the appendedclaims.

I claim-as my invention:

1-. In the method of insulating conductors, in

combination, covering the conductor with a lay-.

er of self-polymerizing materialcontaining an inhibitor, covering thelayer of sell-polymerizing opposing the covered conductor to sumcientheat to cause the layer of material containing the catalyst to hardenwithout causing polymerization of the material containing the inhibitor,and

pressure to cause the material containing the inhibitor to hardemthelayer of material hardened before the polymerization of the materialcontaining the inhibitor preventing vaporization of the materalpolymerized under the heat and pressure.

2. In the method of insulating conductors, in combination, covering theconductor with a plurality of layers of self-polymerizing material,theinner layer of the self-polymerizing material containing an inhibitorand the outer layer containing a catalyst, exposing the coveredconductor to suficient heat to harden the'outerlayer of matetaining aninhibitor associated therewith and the outer layer of the tape having aself-polymerizing? material containing a catalyst associated therewith,subjecting the wrapped conductor to a temperature of at least roomtemperature to harden the material containing the catalyst in the outerlayer of tape without causing polymerization oi the material containingthe inhibitor in the inner layer of the tape, and subjecting theconductor I in the hardened outer layer of tape to heat and pressure tocause the polymerization of the material containing the inhibitor, theouter layer of tape and its associated hardened material preventing lossof the material containing the inhibitor by vaporization during itspolymerization.

imthe method of insulating conductors, in combination, wrapping a layerof tape on the conductor, impregnating the tape with a selfpolymerizlngmaterial containing an inhibitor,

wrapping an outer layer of tape on the tape impregnated with theself-polymerizing material containing the inhibitor, impregnating theouter layer of tape with a self-polymerizing material containing acatalyst, subjecting the wrapped conductor to'a temperature of at leastroom temperature to harden the material containing the catalyst in theouter layer of tape without causing polymerization of the materialcontain-= ing the inhibitor in the inner layer of the tape. andsubjecting the conductor wrapped in the hardened outer layeroi tape toheat and pres sure to cause the polymerization of the materialcontaining the inhibitor, the hardened outer layer or tape preventingloss or the material containing the inhibitor by vaporization during itspoly-= merization.

5. In the method of insulating conductors, inv

combination, wrapping the conductor with a plurality of layers oitape,the inner layer of the tape having a self-polymerizing materialcontaining an inhibitor associated therewith and the outer layer or thetape having a. sell-polymerinng material containing a, catalyst asso=elated therewith, subjecting the wrapped conductor to a temperature ofat least room ternperature to harden the material containing thecatalyst in the outer layer of tape without caus ing polymerization ofthe material containing the inhibitor in' the inner layer or the tape,

wrapping aprotective covering over the hardened outer layer of tape,immersing the conductor in the protective wrapping in a-hotresin andapplying pressure thereto to cause the polymerization of the materialcontaining the inhibitor, the hardened outer layer .of tape preventingloss of the material containing the inhibitor by vaporization during its,polymerization, removing the conductor from the hot resin when thematerial containing the inhibitor is polymerized, and removing theprotectivecovering from the insulated conductor.

6. In the method of insulating conductors, in combination-wrapping .alayer 01 tape on the conductor, impregnating the tape with aselfpolymerizing material containing an inhibitor,

wrapping an outer layer of tape on the tape impregnated with theself-polymerizing material containing the inhibitor, impregnating theouter layer oi tape. with a self-polymerizing material containing acatalyst, subjectingthe wrapped conductor to a temperature of at leastroom temperature to harden the material containing the catalyst in theouter layer of tape without causing polymerization of the materialcontaining the inhibitorin the inner layer of the tape, wrapping aprotective covering over the hard ened outer layer of tape, immersingthe conductor in the protective wrapping in a hot resin andcombination,impregnating tape with a selfpolymerizing material containing aninhibitor,

wrapping the impregnated tape on the conductor. covering the wrappedconductor with an outer layer of self-polymerizing material containing acatalyst, subjecting the covered conductorto a temperature of at leastroom temperature for a period oi time sufflcient to harden the outerlayer of self-polymerizing material without causing polymerization ofthe selfpolymerizing material in the tape wrapping, and subjecting theconductor in the hardened cover'to heat and pressure to cause thepolymerization of the material containing the inhibitor in the tape, thehardened outer covering on the conductor preventing loss of theimpregnating material of the tape by vaporization during itspolymerization.

8. In the method of insulating conductors, in

combination, impregnating tape with a selfpolymerizing materialcontaining an inhibitor,

wrapping the impregnated tape on the conductor, covering the wrappedconductor with an outer layer of self-polymerizing material containing acatalyst, subjecting the covered conductor to a temperature ofat-leastro'om ternperature for a period of time suflicient to harden theouter layer of self-polymerizing material without causing polymerizationof the selfpolymerizing material in the tape wrapping, wrapping aprotective covering over the hardened outenlayer to protect it,immersing the conductor wrapped in the protective covering in a hotresin and applying pressure thereto to cause the polymerization of thematerial containing the inhibitor in the tape, the hardened outerlayerof material preventing loss or the impregnating material of the tape byvaporization during its polymerization, removing. the conductor from thehot resin when the impregnant oi the tape is polymerized, and removingthe protective covering from the insulated conductor.

' JOHN F. CALVERT.

